Contents

Idea

A general circulation model or global climate model (these are synonymous interpretations of the acronym GCM) is a climate model that tries to incorporate all relevant processes on Earth in a three dimensional model. Such models are the most complex ones today.

Grids

Usually the horizontal grid spacing is not the same as the vertical grid spacing. The GCMs mentioned in the last IPCC? report had a horizontal grid spacing of 100-300 km. CGM currently under development aim at 50 km and less.

Earth has a surface of 510,072,000 km2km^2, therefore a homogeneous grid of 50 km horizontal spacing corresponds to ca. 200 000 horizontal grid cells. If there are 25 vertical grid cells, we get ca. 5 000 000 grid cells. If we assume a memory capacity of 1 GB for holding the grid, we have ca. 2 kB per grid cell.

Online Software Projects

AOM

The NASA/GISSAtmosphere-Ocean Model? or AOM was a continually evolving computer program written in Fortran. The website for this project contains files that describe the model, both in English and in algorithm notation, together with the Fortran source code:

ModelE

This involves a complete rewrite of the underlying physics, combined with greater flexibility and better representations of the stratosphere, tracer components and various ocean models.

The frozen version used for IPCC? AR4 simulations is called ModelE1 (internal version number 3.0, dated Feb. 1, 2004). This code can be freely downloaded (as a 1.2 MB gzip-ed tar file). There are nightly snapshots of the current code repository available also, but users should be aware that these snapshots are presented ‘as is’ and are not neccessarily suitable for publication-quality experiments. The frozen AR5 version will be posted soon.

Educational Global Climate Modeling

EdGCM provides a research-grade Global Climate Model (GCM) with a user-friendly interface that can be run on a desktop computer. For the first time, students can explore the subject of climate change in the same way that actual research scientists do. In the process of using EdGCM, students will become knowledgeable about a topic that will surely affect their lives, and we will better prepare the next generation of scientists who will grapple with a myriad of complex climate issues.